1. Field of the Invention
This invention relates to ozone production facilities employing an ozonizer for generating ozone for use in the treatment of clean water and sewage, as well as the bleaching of pulp; and a method of operating the facilities.
2. Description of the Prior Art
FIG. 1 is a block diagram of conventional ozone production facilities. A starting gas 11 (main component: oxygen) prepared by oxygen production facilities 2 is supplied to an ozonizer 3. Ozone 12 generated by the ozonizer 3 is fed to ozone treatment facilities (not shown; e.g., facilities for sewage disposal and pulp bleaching). The concentration of ozone is monitored with an ozone analyzer 4. The amount of ozone generated is calculated by multiplying the flow rate of oxygen (monitored with an oxygen flowmeter 6) supplied to the ozonizer 3 by the ozone concentration.
FIG. 2 is a block diagram of PSA (pressure swing adsorption) type oxygen production facilities, an example of oxygen production facilities. Air in the atmosphere is pressurized by an air blower 32, and fed to one adsorption tower 31 with valves 35 and 37 being opened (with valves 35a and 37a being closed). The adsorption tower 31 is filled with an adsorbent, which adsorbs and removes moisture, carbon dioxide and nitrogen in the air selectively. Oxygen that is minimally adsorbed (the starting gas 11) passes as such through the adsorption tower 31. Then, the oxygen is pressurized to a desired pressure by a compressor 34, and supplied to an ozonizer 3. As the adsorption proceeds, no further moisture, carbon dioxide and nitrogen can be removed. At this time, the valves 35 and 37 are closed, while other valves 35a and 37a are opened to switch from the adsorption tower 31 to another adsorption tower 31a. Simultaneously, a valve 36 is opened to vacuumize the adsorption tower 31 by means of a vacuum pump 33. As a result, adsorbed gas components 13 comprising the adsorbed moisture, carbon dioxide and nitrogen are discharged, whereby the adsorbent is regenerated. By so using the adsorption towers alternately, oxygen can be produced continuously.
FIG. 3 is a graph showing the oxygen concentration as a function of the flow rate of oxygen produced by the oxygen production facilities. The oxygen concentration depends on the flow rate of oxygen and the amount of the adsorbent, and decreases as the flow rate of oxygen increases. For example, let the flow rate of oxygen be 1 for a maximum concentration of 95%. At a relative flow rate of 1.5, the oxygen concentration decreases to 60%.
FIGS. 4A and 4B schematically show a double pipe ozonizer, with FIG. 4A being a sectional view in a direction parallel to the common axis, and FIG. 4B, a sectional view in a direction perpendicular to the common axis. The double pipe ozonizer has a cylindrical stainless steel housing 101, which houses a cylindrical stainless steel ground electrode 102 disposed coaxially, and glass as a dielectric layer 103 in intimate contact with the inner surface of the ground electrode 102, both ends of the ground electrode 102 and the dielectric layer 103 being fixed to the housing 101. At the center of this ozone generation tube, a cylindrical stainless steel high-voltage electrode 104 is coaxially disposed so as to be separated from the surface of the dielectric layer 103 by a discharge space 105. A power source connector portion attached to a part of the electrode 104 extends to the outside of the housing 101, passes through a bushing 106, and becomes connected to one end of the housing 101 through a high frequency power source 107. At the center of both side surfaces of the housing 101, capillaries 111 are passed and fixed. These capillaries 111 are connected to the cylindrical high-voltage electrode 104 via insulating tubes 109. By this arrangement, cooling water 108 is flowed into the high-voltage electrode 104 in the directions of the arrows in the drawing. Cooling water 108 is also introduced from the outer peripheral surface of the housing 101 to cool the ground electrode 102.
From one end of the discharge space 105 of the double pipe ozonizer, the starting gas 11, produced by the aforementioned oxygen production facilities, is supplied. An exhaust valve 110 provided at the other end of the discharge space 105 is adjusted to set the absolute pressure at, approximately, 1.6 atmospheres. An alternating current is applied between the ground electrode 102 and the high-voltage electrode 104 by the high frequency power source 107. As a result, a silent discharge occurs to generate ozone 12. The concentration of the generated ozone 12 is monitored with an ozone analyzer 4. The ozonizer facilities in actual use have several hundred electrodes arranged, therein but their basic structure is the same as the ozonizer illustrated here.
The above ozone production facilities posed the following problems:
Generation of ozone in a large amount requires a large amount of oxygen, the starting material, which in turn requires large-scale and high-cost oxygen production facilities.
Increasing the flow rate of oxygen to the maximum capacity of the oxygen production facilities decreases the concentration of oxygen produced, and also lowers the concentration of ozone.
The concentration of ozone generated by the ozone production facilities is more than 200 g/m.sup.3, which is applicable to pulp bleaching. In the treatment of clean water and sewage, the ozone concentration must be reduced to about 100 g/m.sup.3.